Properties of Exotic Matter

This question really goes from Newtonian mechanics through relativity and quantum mechanics, but this is probably the right place to ask the question. If not I apologize. I have several questions regarding exotic matter, or negative matter. I'll just fire them off in random order.

First off, what form is it most likely to take, if it exists? Is there any possibility it would, or even could, take a solid form?

Is there any relation between negative energy and the dark energy that is accelerating the expansion of the universe?

Is it true that negative matter would be gravitationally repelled by regular matter, and gravitationally attracted to itself? This seems to make sense from a Newtonian standpoint, but I can't reconcile this with the equivalence principle of general relativity. Gravity is, after all, a phantom force. Right?

If I push against an object with negative mass, it won't push back with an equal and opposite force. Instead, it will pull on me with an equal force in the same direction. But wouldn't this create a force feedback loop resulting ultimately in an infinite force?

Is the previous question even relevant, or would the negative mass object simply cancel out the mass of my hands, causing them to simply disappear?

Is there any evidence of negative energy other than the Casimir Effect? How plausible is negative mass? Was it invented mainly as a "sure would be nice" concept to keep wormholes open and Alcubierre drives running? Or are there real reasons to expect it to exist, like supersymmetry maybe?